1. Field of the Invention
This invention relates to computer disk head assemblies, and more particularly to a computer disk head assembly load beam having improved vibrational and torsional stiffness characteristics.
2. Related Art
Magnetic disk drives have become an important part of the computer industry. Typical modern magnetic disk drives have a plurality of flat, circular, spaced apart disks rotating about a common spindle. Data is stored on a magnetic media formed on the surface of the disks. Data is divided into groupings called "tracks" that form concentric rings on the surface of the disks. A read/write head is positioned above each side of a disk. As the disk spins beneath a head, the head can magnetize the magnetic media in a track, thereby writing onto the track. After data is stored on a track, the read/write head can be positioned above a track, and as the disk spins, the head can read back the magnetic pattern stored on the disk track. To write on or to read from different tracks, the read/write heads merely need to be moved towards or away from the spindle.
The read/write heads typically comprise an electromagnetic core and coil mounted on a "slider" which has an air-bearing surface positioned immediately adjacent the flat surface of a disk. As the disk spins, the air following the disk applies pressure to the slider's air-bearing surface, and lifts the slider and read/write core and coil off of the surface of the disk.
The slider body is attached to a component called a flexure. A flexure allows the slider body to gimbal to follow fluctuations in the surface of a disk while restricting the slider's motion in undesired directions with respect to the disk. To support a flexure in the proper position, the flexure is attached to an elongated load beam which in turn is attached to an arm coupled to a carriage in the disk drive. The load beam is generally made of steel and acts as a leaf spring to bias the slider towards a disk.
FIG. 2 shows a typical prior art load beam. Typically, each such load beam 20 comprises an essentially square attachment area 22, with a tapered arm portion 24 which normally is adapted for attaching the further end of the load beam 20 to a flexure (not shown).
Usually, the square attachment area 22 of the load beam 20 is welded to a flat "insert" 26. The insert 26 gives sufficient rigidity and strength to permit conveniently attaching the load beam 20 to an arm of, for example, an "E-block" carriage (not shown), as is known in the art.
It is important that the air-bearing surface of the slider attached to the flexure be substantially parallel to the disk surface. In typical prior art structures, the arm of the carriage is offset from the surface of a disk. Therefore, when the load beam/flexure assembly is mounted in a disk drive, the elongated arm 24 of the load beam is bent at a small angle in order to extend from the carriage arm to near the disk. To compensate for this small angle, the flexure is bent at a small angle to the base of the load beam 20. Thus, the slider's air-bearing is maintained substantially parallel to the surface of a disk.
Over the past several years, the size of disk drives has shrunken considerably, from a 14-inch form factor down to as little as a 21/2-inch form factor at present. While the physical size of disk drives has been shrinking, the density of information storage on the disks of such disk drives has been increasing. Both the number of bits per inch (bpi) and tracks per inch (tpi) have increased significantly over the past several years. Furthermore, the speed of access of the head assembly from track to track in such disk drives has also been increasing, resulting in higher performance disk drives.
As a result of decreasing disk size, increasing data density (in particular, increasing tracks per inch), and decreasing head movement times, the problem of maintaining accurate head position over a selected data track has becoming increasing difficult. This problem is aggravated by the fact that the platter surfaces of disk drives are not perfectly flat. Thus, the spring bias provided by a load beam is important in maintaining a bias on the slider such that the slider maintains an approximately constant distance from its disk as the surface of the disk varies. Maintaining such a constant distance and an accurate head position is extremely difficult if the structure on which each magnetic read/write head is mounted vibrates to such a degree that data reading or writing ability is impaired.
Since all head assembly structures have resonant vibrational modes, one means of reducing undesirable vibration is to increase the resonant frequency for the most fundamental resonant modes to a level higher than is likely to be encountered in a disk drive system. Thus, vibration caused by imbalances in the rotating disk platters, movement of the head assembly across the disk, and other sources can be significantly reduced if the resonant frequencies of the appropriate portions of the head assembly structure can be increased.
For example, it is known that the first resonant mode of load beams such as those of the prior art is an "up and down" motion pivoting around the "spring axis" of the load beam. The second resonant mode is known to be a twisting of the load beam around its longitudinal axis. High-amplitude movements from the first resonant mode are undesirable because they cause fluctuations in the distance of the magnetic read/write head from the magnetic disk surface. The second resonant mode is undesirable because the twisting of the load beam arm causes changes in the length of the arm, which in turn causes the read/write head to move off track. In addition, such twisting may cause a slider to tilt with respect to a disk surface rather than remaining parallel to such a surface. It is therefore desirable to raise the resonant frequency of both the first and second resonant modes of a load beam to a level that is less likely to be encountered in a disk drive environment.
The prior art in the past has used damping material on the flexure portion of a load beam structure to reduce vibration. However, such damping material increases the mass of a load beam, thereby impairing the ability to rapidly move the load beam from one point to another. Adding such damping material also increases the cost of manufacture of the load beam structure.
It is desirable to increase the resonant frequency of such load beams in order to better maintain the position of an attached read/write head over the desired portion of a disk. It is also desirable to maintain spring characteristics in the load beam that are comparable to those known and relied upon by engineers in the art. In designing a load beam, it is also important to maintain both structural rigidity with respect to all degrees of freedom except the necessary up and down motion around the "spring axis" to accommodate variations in the disk surface. It is also desirable to provide a load beam with resonant frequency characteristics such that damping material can be minimized or eliminated.
It is therefore an object of this invention to provide a load beam structure that has a spring rate equivalent to the spring rate of prior art load beams, while having resonant frequencies for at least the first and second resonant modes that are substantially higher than the corresponding resonant frequencies of prior art load beams.